Numerous types of optical waveguides for coupling optical fiber and other optical devices are known. These waveguides may have multiple inputs and outputs or may simply join two similar lengths of optical fiber. In addition, the waveguides may be active (thermooptic or electrooptic) or passive devices. Three important parameters of any optical waveguide are the loss through the device, the refractive index, and the size. Different types (multi-mode, single-mode) and different sizes of optical fibers require different waveguide film thicknesses and indices of refraction to minimize coupling losses into and out of the waveguide. The overall thickness of the waveguide is also important in device design because devices having thinner, higher index cores allow more complex devices, with tighter bends, to be fabricated in the same size package.
Optical telecommunications systems today are large and expensive, requiring racks of equipment to enable full realization of dense wavelength division multiplexing (DWDM) technology. To bring the benefits of optical voice and data transmission closer to the end user, as opposed to current long haul fiber-optic systems, the size and cost of the equipment must be reduced. Currently these systems are comprised of connected single-function components, with most of the cost and size being contributed by packaging and assembly. The coupling of these numerous individual devices also introduces unwanted complexity and signal loss into the overall system. Integration is the key to solving these issues, but methods for addressing this integration are lacking in the prior art. In particular, active waveguide materials often have a higher refractive index than the fiber or passive waveguides, and these materials are formed by different processes, further complicating integration. Thermooptic active devices may be formed from lower index waveguide materials similar to those used in the fiber core, but these devices typically operate at millisecond switching speeds or slower, whereas electrooptic devices, which operate at sub-nanosecond switching speeds and are therefore desirable for many high-speed applications, are generally very difficult to integrate onto wafers or chips containing passive devices. It is also difficult to achieve efficient coupling of current electrooptic devices with telecommunications-grade optical fibers, because of the differences in cross-sectional area between the fiber and the waveguide.